Negative transconductance electrical discharge tube



May 17, 1949.

Flled Nov. 5, 1943 2 m, 3 N mm. H 7, ww M m m WE w. 4 w nlm. E ...w wl M n f, T .wu fu m R m m l s I D /W W Rm tv R H w 5 m y E f M .L n n L C u Jm w o w m R T E w T A G E N May 17, 1949.

Flled Nov. 5, 1945 2 3 n t mm r fu M .m mlm Mm m 4, b wm M 2 d w .M S s a 3 M Y W B J. F. vrsscl-IER NEGATIVE TRANSCONDUCTANCE ELECTRIQAL DISCHARGE `TUBE May 17, 1949.

Flled Nov 5, 1945 Patented May 17, 1949 NEGATIVE TRNSCONDUCTANCE ELECTRI- CAL DISCHARGE TUBE .l uan Francisco Visscher, Buenos Aires, Argentina, assignor to Hartford National Bank and Trust Company, Hartford, Conn., trustee Application November 5, 1943, Serial No. 509,136

4 Claims. l

This invention relates to a negative transconductance tube and more particularly to a tube in which negative transconductance characteristic between the output and control electrodes is accompanied by a high internal resistance between the output electrode and the cathode of the tube,

@ne of the most widely used methods for obtaining a negative transconductance in a tube without utilizing the secondary emission phenomenon is to connect a known high-vacuum multigrid tube so that a rise in potential on the control electrode causes a decrease in the ilow of electrons to the output eiectrode of the tube. The so-called Transistron represents one of the known negative transconductance tubes and though it is particularly useful as an oscillator, the negative transconductance characteristic thereof only extends over a relatively limited operating range of the control grid voltage. Furthermore, the internal resistance between the anode and the cathode of a Transistron in the negative transconductance range is relatively low. in general, it may be stated that the known negative transconductance tube may be repren sented as triodes, that is having a low ampliiication factor and a relatively low internal resistance between the output electrode and the cathode.

I have found, however, that the characteristic features of a pentode tube, that is a large amplilisation factor and a high internal resistance can be reproduced in a negative transconductance tube by providing a tube, having a cathode, a plurality oi auxiliary electrodes and an anode, with an output electrode formed by two rod-shaped members located within a control electrode constructed as grid, the auxiliary electrodes separating the output electrode from the cathode and control electrode.

By connecting the electrodes of the tube to adequate potentials and by suitably shaping the auxiliary and output electrodes, the electrons emitted by the cathode are shaped into beams and reach the output electrode after having been repelled by the electrical eld existing in the vicinity of the control electrode, so that the majority of the electrons drawn into the output electrode are moving along indirect paths within the electrode system of the novel tube.

Due to the particular arrangement of the electrodes there is practically no direct flow of electrons from the cathode towards the output electrode or plate, and they plate current of the tube will be determined entirely by the voltage applied to the control grid since a decrease in the voltage (Cl. Z50-27.5)

applied to the control electrode, that is an increase in its negative value, will produce a stronger electrical eld in the vicinity of the control electrode which by repelling a greater number of electrons towards the output electrode, will cause a corresponding increase in the 'output or plate current of the tube.

Thus a tube is obtained, the negative transconductance characteristic of which extends over the whole range of normal polarization potentials of the control electrode and which at the same time, has a high internal resistance between the output electrode and the cathode.

The novel principles and features of my invention are set forth in the appended claims; the invention itself, however, as to the arrangement of the electrode and method of operation of the tube will be best understood by reference to the description taken in connection with the drawings forming part of this specification and wherein Fig. 1 diagrammatically represents the electrodes of a tube constructed according to one embodiment of the invention.

Fig. 2 is a graph showing by way of eXample the static potentials applied under operating conditions to the electrodes of the tube shown in Fig. i.

Fig. 3 illustrates a modification of the tube according to the invention.

Fig. 4 shows still another modification; and

Figs. 5 and 6 are schematic diagrams `of circuits incorporating the electrical discharge tube according to the invention.

Referring now to the accompanying drawings, wherein like reference characters in the' different iigures designate similar elements or parts, it can be seen that the tube 42 in Fig. 1 comprises a flat cathode l0 surrounded by two auxiliary concentric electrodes constituted by the circular grid structures l2 and lll respectively, said grid structures being supported by the corresponding pair of rods i6 or i8 located in a plane passing through the cathode l il of the tube.

The output electrode of the tube is constituted by two rod-shaped members 2D, each provided with a collector plate 212 and located outside the auxiliary grid I4. The output electrode 22 is surrounded by a third auxiliary electrode 24 and a control electrode 26 both concentrically arranged with respect to theauXiliary electrodes by circular grid structures 24 and respectively, each grid structure being supported by the corresponding rods 28 or 30 as shown in Fig. 1. The supporting rods t8, I8-, 28 and 30", together with the rod-shaped members 20 of the output electrode 22 are arranged in a common plane passing through the cathode l of the tube, the electrode system of which is surrounded by a circular anode A.

The static electrode voltages of the novel tube under usual operating conditions are shown in the graph in Fig. 2, where it can be observed that a very low positive potential of approximately l volt is applied to the auxiliary electrode l2, in order to obtain an initial acceleration of the electrons and to avoid the formation of a space charge in the vicinity of the flat cathode lil, so that the only possible virtual cathode of the tube will be that formed by the control grid 24, the operation of auxiliary grid 26 being similar to that of the field grid in old tetrodes. Auxiliary electrodes i4 and 24%, which form the screen grids between the output electrode 22 and the cathode lll control electrode 26 respectively, are connected to somewhat higher positive potentials of approximately 30 volts, Iwhile the output electrode 22 and anode A are connected to a high positive potential of approximately 300 volts. Under normal operating conditions the voltage of the control grid 26 may vary between zero and minus 5 volts approximately.

Those skilled in the art will readily understand that thanks to the particular arrangement of the electrodes within the tube and more particularly to the arrangement of the ilat cathode ill in a common plane with the supporting rods of the auxiliary grid structures, the majority of the electrons emitted by the cathode in tWo opposite beams, are not directly attracted by the output electrode 22 but move towards the anode A which, as mentioned above, is connected to a source of high positive potential. However, the electrical lield built up in the vicinity of the control electrode 26 as a consequence of the low potential gradient thereof, slows down and repels the approaching electrons which, attracted by the high potential eld of the output electrode are drawn into the collector plates 22.

It is obvious that an increase in the negative voltage applied to the control grid 22 will produce a stronger repulsive eld in the vicinity of said electrode and consequently a greater number of electrons will 'be repelled and drawn into the collecting plates of the output electrodes 22, causing a corresponding increase in the current flowing in the output circuit of the tube.

However due to the fact that the only screening means interposed between the output electrode 22 and the cathode Il! are constituted by the supporting rods i8 of the auxiliary grid structure ill, the output current of the tube shown in Fig. 1, comprises not only the electrons which move along the indirect paths indicated by reference 32 and which are controlled by the control electrode 26, but also electrons flowing directly from the cathode lll to the output electrode 22 along the direct paths 313 which are not controlled by the potential applied to the electrode. Therefore the internal resistance of the negative transconductance tube i2 shown in Fig. l and its amplication factor are relatively low.

The above-mentioned limitation restricting the internal resistance and the amplication factor to relatively low values has been completely overcome in the electric discharge tube 42a shown in Fig. 3 in which the general arrangement of the electrodes is similar to that of the tube ft2 in Fig. l. However, in order to prevent the direct flow of electrons between the cathode l0 and the output electrode 22, the auxiliary electrode lll is provided with diametrically opposed shielding plates or electron deflecting means lll which are soldered to the supporting rods lll and are adapted to the curvature of the grid structure it of said electrode lli.

The output electrode of the tube 52a is formed by two collector plates 22', soldered to the supporting rods 2li placed at either side of the flat cathode lu and located in a plane passing through said cathode and the supporting rods of the other auxiliary electrodes of the said tube. The cross-section of collector plates 22 is almost parabolic, and their virtual longitudinal axes are substantially parallel to the virtual longitudinal axis of the electrode system of the tube. At the same time, said collector plates 22', are bent towards the flat cathode lll, so that their lateral edges 23, are quite close to shielding strips iii of the auxiliary electrode, and are completely screened with respect to the cathode it by said shielding strips lll which thus prevent the direct flow of electrons between said output electrode 22 and cathode lil of the tube.

The shielding strips lll of the auxiliary electrode not only prevent the direct flow of electrons from the cathode l@ to output electrode 22, but also facilitate the shaping of the indirect paths of the electrons which are emitted by the cathode l@ in two main opposite beams 365. To further the shaping of the electron beams Sil and to ensure that all electrons repelled by the electrical field of the control electrode 2t', are drawn into the collector plates 22 of the output electrode 22', the grid structure 2e' of the the auxiliary electrode 2li' and the anode A j are of a substantially oval cross-section, the

smaller axis of said anode A being located in a plane passing through the cathode l!) and comprising the supporting rods of the other auxiliary electrodes of the tube, while the larger axis of the anode A coincides with the smaller axis of the oval grid structure 2li of the auxiliary grid, so that the circular grid structure 26 of the control electrode, and said auxiliary electrode, are relatively close together in the vicinity of their supporting rods, but are further apart in a direction perpendicular to the plane passing through the cathode IU and comprising the supporting rods of the auxiliary electrodes of the tube. On the other hand, the oval grid structure 2 is quite close to the grid structure hl of the auxiliary electrode, in the same direction.

Thus the lines of force of the electrostatic field within the electrode system of the tube are distributed so as to divide the main beams 34 into two beams 36 so that the electrons of said beams, when repelled by the electrical field of the control electrode, are inevitably drawn into the corresponding collector plates 22 of the output electrode 22.

As already explained hereinbefore, there is no direct flow of electrons between the cathode l0 and the output electrode 22 of the tube 5241, due to the screening eiect of the shielding plates It of the auxiliary electrode I4', and consequently the control oi' the output or plate current of the electrode 22 by the potential applied to the control grid is almost perfect. Therefore, the tube shown in Fig. 3 has not only a, negative transconductance between the output electrode 22 and the control electrode but also a very high internal resistance between the output electrode and the cathode, so that said tube incorporates the characteristic features of positive transconductance pentodes.

In order to obtain a still better shaping of the electron beams 34', the control electrode gc is provided with diametrically opposed deecting ribbons 26 located in a plane comprising the longer axis of the anode A and the space changes created in the vicinity of said ribbons 26 deect the approaching electrons in lateral directions towards that region of the control electrode ge from which a return of the electrons to the collector plates 22 of the output electrode 22' is ensured.

The direct flow of electrons from the cathode I Il to the output electrode 22 of the tube may also be prevented by inserting an intermediate electrode 35 between the rst and second auxiliary electrodes respectively. The intermediate grid 35 of the tube 4217 of Fig. 4 is formed of four rods 35, their sections being located at the corners of a rectangle, the larger Virtual axis of which passes lengthwise through the cathode and the supporting rods of the auxiliary electrodes of the tubes. Such intermediate electrode 35 is usually connected to a high negative potential so that the relatively strong electrical fields built up in their vicinity prevent the direct flow of electrons towards the output electrode 22' of the tube 4217, said rods 35 of the intermediate electrode gl thus acting as electric shields with respect to the output electrode 22'.

The negative transconductance tube according to the present invention is particularly useful inv variable reactance circuits of the type described in prior U. S. patent application Serial No. 481,499, led April 1, 1943, entitled YElectronically variable reactance, now abandoned, in which a reaction circuit comprising a positive transconductance relay tube is used, in order to make the access impedance of the reaction circuit independent oi the transfer characteristic of the circuit.

However, the performance of the variable reactance circuit described in the aforementioned patent application is somewhat limited, owing to the fact that the positive transconductance of the tube used in the reaction circuit may not exceed a certain maximum value, since for some frequencies the real part of the created admittance Y" may easily become zero or even acquire negative values.

In fact, the real part of the created admittance Yo is substantially proportional to the sum of the internal conductance of the utility tube and the input admittance of the reaction quadripole minus the product of the transconductances of the relay and the utility tubes divided by the change admittance. As both tubes used have positive transconductance characteristics, this product may easily become nearly equal to the sum of the other factors, so that the auto-oscillation of the electronically variable reactance circuit is made possible.

The above-mentioned limitation is not present in the electronically variable reactance circuit shown in Fig. 5, in which the reaction circuit, indicated by the general reference number 40, comprises a negative transconductance relay tube 42 inserted between an entrance section 44 and a pass Section 46 coupled to the control grid of the positive transconductance utility tube 48.

As explained in the said prior patent application No. 481,499, the utility admittance of the Cil general circuit comprises an active part formed by the sum of the access conductance of the entrance section 44 and a reaction conductance, and a reactive part which is the sum of the access susceptance of said entrance section 44 and a reaction susceptance, the reaction conductance and reaction susceptance being dened by the nature of pass section 46 and proportional to the product of the transconductances of the relay tube 42 and utility tube48. However, since said product of both tube transconductances is now positive, the generation of auto-oscillation in the circuit is almost completely avoided.

As previously stated, the negative transconductance characteristic of the tube 42, according to the present invention, is present between the output electrode 22 and the control grid 2li and is determined by the indirect flow of electrons from the cathode I9 to said output electrode 22 of the tube. It is obvious, however, that not all of the electrons emitted by the cathode Ill are repelled by the electrical field existing in the vicinity of Said control electrode 26, and that a certain number of electrons may pass through the meshes of the control electrode grid structure 2lil and be drawn into the anodes A or A.

It can be readily understood that the number of electrons flowing from the cathode IB to the anodes A or A of the tubes 42 and 42a will be controlled by the potential applied to the control electrode 23 and that an increase in the negative voltage of said control electrode will naturally cause a decrease in the number of electrons flowing towards the anode of the tube, while simultaneously. increasing the number of electrons drawn into the negative transconductance output electrode 22 or 22.

Therefore, a signal voltage applied to the control electrode 26 is cophasally amplified in the circuit of the output electrode 22 or 22', while the voltage developed in a circuit connected to the anode A or A will be 180 out of phase with respect to said signal voltage applied to the control grid of the tube.

The tube according to the present invention canconsequently be utilized in a combined phaseinversion and push-pull output circuit shown schematically in Fig. 6, wherein the input terminals 'I4 and 13 are connected to a grid-leak resistance 'I8 of the control grid 26 while the output electrode and anode A of the negative transconductance tube 'i9 are connected to the opposite ends oi the primary winding Bil of a pushpulloutput transformer T. The electric mida point of said primary winding 8B is connected to the positive pole of a direct current supply l5 from which the' corresponding supply voltages for the auxiliary yelectrodes of the tube are also derived. Secondary winding 84 of said transformer T is connected to the output terminals 83 and 98 of the circuit.

As indicated in Fig. 6, the negative transconductance tube 19 used in the phase inversion push-pull output circuit comprises an additional auxiliary electrode g4 inserted between the control electrode 2G and anode A. By connecting this additional auxiliary electrode externally or internally to the other auxiliary electrodes of the tube or to a suitable positive potential, the flow of electrons in the output circuits of the electrode go and anode A can be controlled so as to obtain as perfect a balance as possible of the push-pull output voltages developed across the primary winding ll of the transformer T.

Although the present invention has been described with particular reference to certain preferred examples, it is to be understood that various modifications may be made in the arrangement and construction of the tube electrodes, without thereby departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A negative transconductance tube comprising a cathode, an output electrode comprising two rod-shaped members placed at opposite sides of said cathode substantially in a plane through said cathode and plate members on said rod-shaped members, an anode, a control electrode adjacent to and surrounded by said anode and surrounding said rod-shaped and plate members and said cathode, rst and second auxiliary electrodes, said first auxiliary electrode surrounding said cathode and said second auxiliary electrode surrounding said irst auxiliary electrode and separating said output electrode from said cathode, a third auxiliary electrode interposed between said output electrode and said control electrode, said second auxiliary electrode having diametrically opposed shielding plates having longitudinal axes arranged substantially parallel to the longitudinal axis of the electrode system of the tube and being located in said plane, said shielding plates being placed to shield said output electrodes from the direct ow of electrons from said cathode.

2. A negative transconductance tube comprising a cathode, a rst auxiliary electrode, a second auxiliary electrode surrounding said iirst auxiliary electrode, a third auxiliary electrode surrounding said second auxiliary electrode, a control electrode surrounding said third auxiliary electrode, an anode surrounding said control electrode, an output electrode interposed between said second auxiliary electrode and said third auxiliary electrode and comprising a pair of rod shaped members and a pair of collector plates substantially parabolic in crosssection and concave to each other, said rst and second auxiliary electrodes each comprising a circular grid supported by diametrically opposite rods, said rods and rod-shaped members being located in a plane passing through said cathode, said second auxiliary electrode having diametrically opposed shielding plates conformed to the grid structure thereof and placed to shield said output electrode from the direct flow of electrons from said cathode.

3. A negative transconductance tube comprising a cathode, a rst auxiliary electrode comprising a circular grid surrounding said cathode, a second auxiliary electrode comprising a circular grid surrounding said rst auxiliary electrode, a third auxiliary electrode comprising an oval grid surrounding said second auxiliary electrode, a control electrode comprising a circular grid surrounding said third auxiliary electrode, an oval anode surrounding said control electrode, and an output electrode interposed between said second auxiliary electrode and said third auxiliary electrode and comprising a pair of rodshaped members lying substantially in a rst plane passing through said cathode, each of said auxiliary electrodes, said control electrode, and said anode being concentrically positioned, said anode having the larger axis of its oval in a second plane normal to said iirst plane, said control electrode further comprising diametrically opposite reflector ribbons conformed to the grid of said control electrode, and positioned in said second plane, the larger axis of said oval of said third auxiliary electrode lying in said rst plane, said second auxiliary electrode further comprising shielding plates conformed to the grid structure of said second auxiliary electrode and positioned to shield said output electrode from the direct flow of electrons from said cathode.

4. A negative transconductance tube comprising a cathode having a reference plane passing substantially through said cathode, a rst auxiliary electrode comprising a circular grid structure surrounding said cathode, a second auxiliary electrode comprising a circular grid structure surrounding said rst auxiliary electrode, an output electrode comprising two rod-shaped members placed on opposite sides of said cathode and lying substantially in said plane, means interposed between said cathode and said output electrode preventing the direct ow of electrons from said cathode to said output electrode, a third auxiliary electrode surrounding the said output electrode and said second auxiliary electrode and comprising an oval grid structure having its larger axis substantially in said plane, a control grid surrounding said third auxiliary electrode and comprising a circular grid structure and two diametrically opposed reilector ribbons conformed to said grid structure, said ribbons lying substantially in a plane perpendicular to said reference plane, and an oval anode surrounding said control electrode and having its larger axis substantially perpendicular to said reference plane.

JUAN FRANCISCO VISSCHER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,159,765 Jonker et a1. May 23, 1939 2,181,909 Peterson Dec. 5, 1939 2,219,102 Herold Oct. 22, 1940 2,235,817 Freeman Mar. 25, 1941 2,252,580 Rothe et al. Aug. 12, 1941 2,274,648 Bach Mar. 3, 1942 

